Skin fibroblasts from human controls or from patients with familial dysautonomia (FD) have been grown in tissue culture. Beta-Nerve growth factor (NGF) has been measured in extracts from both type of cells, using a radioimmunoassay and a bioassay. The FD cells have contents of NGF as measured by RIA comparable to the controls. However, the biological activity of the FD samples is about one-tenth that of the controls when expressed as biological units of activity per ng Beta-NGF as measured in the RIA. Stimulation of Beta-adrenergic receptors in both cell lines with 1-isoproterenol results in a 17-170 fold rise in intracellular cyclic AMP in 10 min. The NGF content of the control fibroblasts increased 50-300% after 3-4 hrs of exposure to isoproterenol whereas there was no change in the NGF content of the FD cells at any time. The NGF of heterozygote parents is comparable to that of controls, whereas the NGF of amniotic fluid fibroblasts has a lower activity. Assays are being carried out on fibroblasts from women at risk for FD, to determine the feasibility of prenatal diagnosis.